1. Field of the Invention
The present invention relates to a resist top coat composition and to a patterning process using the composition thereof.
2. Description of the Related Art
As LSI progresses toward a higher integration and a higher processing speed, miniaturization of a pattern rule progresses rapidly. In background of this rapid progress of miniaturization, there exist shifting of a projection lens to a higher NA, improvement of a resist composition performance, and shifting to a shorter wavelength.
General use of a resist composition for a KrF excimer laser (248 nm) started in a 0.3-μm process; and this has been used until mass-production of a 0.13-μm rule. Shift to a shorter wavelength from a KrF excimer laser to an ArF excimer laser (193 nm) makes it possible to miniaturize a design rule till 0.13 μm or less; but because a resin such as a novolak resin and a polyvinyl phenol resin, which have been used in the past, has strong absorption near 193 nm, they cannot be used as a resist base resin. To secure transparency and necessary dry etching resistance, an acryl resin and a cycloolefin-based alicyclic resin have been investigated; and as a result, mass-production of a device using an ArF lithography was realized.
In the next 45-nm node device, wavelength of exposure light was made shorter; and thus, an F2 lithography of 157 nm became a candidate for this. However, this has many problems such as cost-up of a scanner due to large consumption of expensive CaF2 single crystals in a projection lens, change of an optical system due to extremely poor durability of a soft pellicle thereby leading to introduction of a hard pellicle, and decrease of resist etching resistance; and thus, postponement of an F2 lithography and early introduction of an ArF immersion lithography were proposed, with which a 45-nm node device is produced in a large scale. For mass-production of a 32-nm node device, a double patterning process using a side-wall spacer is used; but there is a problem of a long and complicated process thereof.
In a device after 32 nm, not an expensive double patterning process but an extreme UV (EUV) lithography of 13.5 nm, resolution thereof being improved by shift of the exposure light to a shorter wavelength by more than one digit, is wanted; and thus, development of it is progressing.
In the EUV lithography, power of a laser is weak and amount of light is decreased because of attenuation of a reflective mirror light; and thus, light intensity reaching to a wafer surface is low. To acquire throughput with a low light intensity, development of a highly sensitive resist is an urgent task. However, if resist sensitivity is enhanced, there is a problem of deterioration in edge roughness (LER and LWR); and thus, a trade-off relationship with the sensitivity is pointed out.
The EUV resist has a problem that it is easily affected from an environment because of its high sensitivity. Usually, an amine quencher is added in a chemically amplified resist to ease the effect of an amine contamination in an air; but amount of the amine quencher added in the EUV resist is a few percentages as compared with the ArF resist and so forth. Accordingly, the EUV resist is prone to form a T-top configuration by receiving the effect of an amine from the resist surface.
To shut the environmental effect, formation of a top coat on a resist upperlayer is effective. In a chemically amplified resist of an early type for a KrF excimer laser based on a t-BOC-protected polyhydroxy styrene, which was not added therein an amine quencher, use of a top coat was effective. In an early stage of an ArF immersion lithography too, a top coat was used to prohibit elution of an acid generator into water thereby avoiding a T-top configuration caused therefrom.
Here, in the EUV lithography process too, proposal was made to form a top coat on the resist upperlayer (Patent Document 1, Patent Document 2, Patent Document 3, and Nonpatent Document 1). By forming a top coat, environmental resistance can be improved and an outgoing gas from a resist film can be reduced.
From an EUV laser of DPP (Discharge Produced Plasma) and LPP (Laser Produced Plasma), in addition to the light of 13.5 nm which is used for patterning, a broad light of 140 to 300 nm (out-of-band, OOB) is oscillated, though is weak. Although intensity of the broad light is weak, but energy amount of this light cannot be neglected because of its wide wavelength range. A Zr filter is provided to an EUV microstepper to cut the OOB light, but this decreases a light intensity. In an EUV scanner in which, to improve throughput, decrease of a light intensity is not allowed, there exists a possibility of not using this filter.
Therefore, development of a resist which is not sensitive to OOB but sensitive to EUV is necessary. As to the resist like this, a cationic structure of a sulfonium salt of PAG is important; and in paragraph [0052] of the Patent Document 5, a bound type acid generator having a low sensitivity to the OOB light but having a high sensitivity to the EUV light is described. In Nonpatent Document 1, superiority of forming a top coat to shield the OOB light on the resist upperlayer is shown.
In the case of a top coat for an immersion lithography, it is pointed that a solvent for a top coat dissolves surface of a resist film thereby causing mixing between the top coat and the resist film, and this in turn causes film loss of a resist pattern after development (Patent Document 4). Especially, when an alcohol solvent is used, film loss is eminent. It is shown that an ether solvent is effective to inhibit film loss. As to a polymer which is soluble in an ether solvent, a polymer which contains a hexafluoroalcohol (HFA), as described in the Patent Document 4, may be mentioned. However, a fluorine atom has a strong absorption to the EUV light; and thus, if a HFA-containing polymer is used as a top coat of a resist upperlayer, there is a problem of lowered resist sensitivity after patterning.
A positive resist having a truxene structure is proposed (Patent Document 6). A resist based on a truxene having a hydroxyl group thereof substituted with an acid labile group is introduced as the EB (electron beam) resist and the EUV resist having excellent etching resistance. Among the underlayer materials having a plurality of bisphenols and excellent etching resistance, a truxene bisphenol compound is shown (Patent Document 7).